1. Technical Field
The present invention relates, in general, to a universal serial bus (USB) hub, and more particularly to a USB hub having a plurality of input power sources which are capable of using bus power or self-power as power for the USB hub in accordance with a user's selection.
2. Related Art
The term "USB" relates to a standard for a universal-type serial bus. In order to facilitate connections between an existing personal computer and peripheral equipment, and in order to cope with a future multi-media environment, such companies as Intel, Microsoft, Compaq and NEC developed a common spec in which transmission speed reaches, at a maximum, 12 Mbps.
The term "USB hub" signifies hardware that serves as a medium for connecting peripheral equipment (a maximum of 127 in number) to a single personal computer in accordance with a USB standard. It provides both data and power distribution.
The cable connection topology of the USB has a construction which amounts to branching through the USB hub. At the lower part of the USB hub, it is possible to connect a function or another USB hub, resulting in a multi-star type topology.
As to the topology described above, a main body of the personal computer having a root hub is placed at the uppermost part thereof, and a hub controller provided in the main body of the personal computer provides communication between USB hubs.
The USB hub functions to carry out its internal function or to distribute power supplied to other hubs and functions connected at the lower part. Thus, the USB hub is supplied with bus power Vbus (upstream power from an upper hub) through a USB cable, or is supplied with self-power Vself from a local power supply unit (an additional independent power supply unit) through a power cable.
Hereinafter, the above-described USB hub supplied with bus power is termed a "bus power USB hub", and the USB hub supplied with self-power is termed a "self-power USB hub".
As described in more detail below, under certain conditions, a user needs a bus power USB hub. Under other conditions, a self-power USB hub is needed or will suffice. Whether or not the user is able to obtain one type of USB hub or the other is sometimes dependent on which type is manufactured and/or provided by the manufacturer.
Thus, there is a need for a USB hub having a plurality of power sources, wherein the user can conveniently select the power source between a local power source or an upstream cable, and can use the selected power source for internal power requirements or for distribution of power to other USB functions.